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Unformatted text preview: BIOLOGY 1107 LECTURE # 42 04-23-10 The Origin of Species Chapter 24 Speciation , the origin of new species, is at the focal point of evolutionary theory Evolutionary theory must explain how new species originate and how populations evolve Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level What is a species? • Members of a biological species are a population of organisms that preferentially interbreed under natural conditions. Father a Tiger/mother a Lion Liger Father a Lion / mother a Tiger Similarity between different species. Diversity within a species. • Speciation is the origin of new species. • Microevolution consists of adaptations that evolve within a population, confined to one gene pool • Macroevolution refers to evolutionary change above the species level • Two basic patterns of evolutionary change: – Anagenesis (phyletic evolution) transforms one species into another – Cladogenesis (branching evolution) is the splitting of a gene pool, giving rise to one or more new species Anagenesis Cladogenesis The biological species concept emphasizes reproductive isolation Reproductive Isolation • Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile hybrids • Two types of barriers: prezygotic and postzygotic • Prezygotic barriers impede mating or hinder fertilization if mating does occur: – Habitat isolation – Temporal isolation – Behavioral isolation – Mechanical isolation – Gametic isolation • Habitat isolation : Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers •...
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